Electro-oxidative method for the recovery of molybdenum from sulfide ores

ABSTRACT

This invention relates to a method for the dissolution of molybdenum and rhenium values in a sulfide-type source. These values are placed in a soluble and available form by pulverizing the source in a aqueous salt solution and electro-oxidizing it in an electrolytic cell.

United States Patent Scheiner et al.

['11] 7 3,849,265 [4 1 Nov. 19, 1974 1 ELECTRO-OXIDATIVE METHOD FOR THE RECOVERY OF MOLYBDENUM FROM SULFIDE ORES [75] Inventors: Bernard J. Scheiner; Roald E.

Lindstrom, both of Reno, Nev.; Thomas A. Henrie, Silver Spring, Md.

[73] Assignee: The United States of America as represented by the Secretary of the Interior, Washington, DC.

[22] Filed: Oct. 1, 1971 [2]] Appl. No.: 185,502

[52] US. Cl 204/86, 204/82, 204/105 R [51] Int. Cl C01b 15/00 [58] Field of Search 204/86, 108, 105, 94, 107,

[5 6] References Cited UNITED STATES PATENTS 410,228 9/1889 Wiswell 204/94 Lukasik 2,761,829 9/1956 Dolloff 204/112 X 3,464,904 9/1969 Brace 204/105 R 3,639,222 2/197-2 Scheiner et al. 204/105 R 3,673,061 6/1972 Kruesi 204/105 R 3,755,104 8/1973 Kruesi 204/94 OTHER PUBLICATIONS Khryashchev et al., Chemical Abstracts, Vol. 70, N0. 4, Abstract 136180, (p. 157), Jan. 1969.

Primary Examiner-F. C. Edmundson Attorney, Agent, or Firm-William S. Brown; Frank A.

[ ABSTRACT This invention relates to a method for the dissolution of molybdenum and rhenium values in a sulfide-type source. These values are placed in a soluble and available form by pulverizing the source in a aqueous salt solution and el'ectro-oxidizing it in an electrolytic cell.

5 Claims, 1 Drawing Figure l SURGE 8 AGITATION TANK PATENTE'U um I 91974 BIPOLAR ELECTROLYTIC SURGE a AGITATION CELL TANK 9 FRESH SLURRY uoum- Y souo DEPLETED TO DISCARD SEPARATOR ORE TA'LS AQUEOUS BRINE MOLYBDATE SOLUTION 19 I6 |o- H I RECOVERED EXCHANGE MOLYBDENUM UNIT VALUES 2| BR'NE f TO RECYCLE BERNARD J. SCHEINER ROALD E. LINDSTROM THOMAS A. H'ENRIE INVENTOR.

ATTORNEY ELECTRO-OXIDATIVE METHOD FOR THE RECOVERY OF MOLYBDENUM FROM SULFIDE ORES BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a novel and effective method for the recovery of molybdenum and rhenium from sulfide ores, concentrates or tailings. More particularly, it relates to the dissolution of molybdenum and rhenium values in sulfide and associated source materials by an electro-oxidation process.

The major sources of molybdenum and rhenium are sulfide-type ores and the like. The classical recovery method is the use of multi-stage flotation techniques and roasting. This recovery method suffers from a number of disadvantages. Multi-stage flotation processes are relatively costly, molybdenum recovery is frequently low, and the roasting of sulfide concentrates causes heavy pollution of the atmosphere. A further disadvantage of the roasting of sulfide ores is that rhenium values are volatilized and go out the stack.

The leaching of molybdenum and rhenium values from sulfide sources has been studied by various investigators. However, in the present state of the developtrated in the flow diagram of FIG. I, a process unit 5 comprising a bipolar cell, 3, and a stirred surge and agiment of the method, the reagent costs alone for hypochlorite and base makes this alternate recovery unattractive.

THE INVENTION It has now been found that molybdenum and rhenium can be converted to a soluble form and extracted from their ores by an electrolytic oxidation method. In the method, an aqueous slurry of a solid sulfide-type source comprising molybdenum, rhenium, or molybdenum and rhenium, is electrolyzed while maintaining the pH of the slurry in the range 1 to 11.5, preferably 5.5 to 9. The carrier liquid for the slurry is an aqueous brine or diluted aqueous brine solution.

In the method of the invention only a nominal concentration of hypochlorite, usuallyless than about 0.2 weight percent, is generated. Nevertheless and surprisingly, in view of the art [see for example Studies in Hypochlorite Leaching of Molybdenite by R. B. Bhappu, D. H. Reynolds, and W. S. Stohmann, Unit Processes in Hydrometallurgy, v 24, pp. 95 113, Gordon & Breach Science Publishers, NY. (1963)] substantially quantitative solution of the molybdenum and rhenium values occurs, especially at slurry pH values in the range 5.5 to 9. Apparently the mechanism in the oxidation of the invention differs from that of the chemical hypochlorite leaching process. Applicants believe that, substantial oxidation takes place at the anode by their method.

By a solid sulfide-type source as used herein is meant by definition, molybdenum sulfide (M08 or rhenium sulfide containing ores and sulfide ores containing molybdenite or rhenium sulfide as a component, for example, copper sulfide ores and the like, flotation concentrates of sulfide ores, ore tailings and the like.

The FIGURE is a schematic flow diagram illustrating a particular mode of the invention, utilizing a bipolar flow-through cell for the electro-oxidative dissolution of the molybdenum present in a sulfide ore.

tation tank 7 are joined by suitable transfer lines 4, 8, 9 and 2 and the unit is used in the electro-oxidation of an aqueous slurry (pulp) of a typical low-grade molybdenite ore, for example an ore containing about"0.2 weight percent of molybdenum sulfide, minor amounts of copper sulfide, iron sulfide and sulfur and having as the major components quartz and potassium feldspar. Via lines 1, 2 and l, 8, 9, a slurry of'the ore is charged to the cell 3, and the surge tank, 7. The liquid component of the slurry is an aqueous brine solution containing about 10 weight percent chloride. The solid component of the slurry is the above described ore which has been pulverized to below 35 mesh (US. Standard Mesh) with about percent of the solid being below 200 mesh. Each 100 parts by weight of the slurry desirably contain about 10 parts of the pulverized ore.

During the electro-oxidation, by means of suitable pumps not shown, the slurry is circulated as indicated,

inluding introduction of the circulative slurry into thecell at the base, via lines 9, 8 and 2, thence up through the bipolar (graphite) electrodes and then withdrawal from the cell via line 4 for delivery to the stirred surge tank 7.

For the electro-oxidation, the following conditions are employed:

Current density, amps/ sq. inch 0.5 Power consumption, kw/hrs/lb of Molybdenium Extracte 25 Slurry pH 5.5-6/5 Slurry Temp, "C 30-60 Time, Average slurry residence time in cell, hours 3.5

with the pH being maintained by the addition via line 5 of solid sodium carbonate (Na CO .H O) as required (total consumption rate of 5 lbs. per lb. of Molybdenum dissolved).

Under the above conditions plus percent of the molybdenum sulfide values in the ore are converted to the soluble salt, sodium molybdate. Where the ore contains a rhenium sulfide component, it too is dissolved v xchange unit 19, via line 15, [see for example; (1) 151 7' Exchange Technology by G. Nachad and J. Schubert, Academic Press, N.Y., 1956; (2) Modern Methods for the Separation of Rarer Metal Ions, (p 506) by Korkisch, J., Pergarnon Press (1969); (3) Anal Chem, (v 36, p 1654) (1964) by Hamaguchi, H., Kawabuchi,pK., and Kuroda, R.; and (4) J. of Chromatography, (v 17, p 567) (1965) by Hamaguchi, H., Kawabuchi, K., and Kuroda, R.; or a liquid-liquid extraction, see for example Zeitschrzft Chemi (v 8, p 235 (1968) by Fisher, C.,

Muhl, P. and Gunzler, G.]. The brine, essentially stripped of its molybdenum content, is withdrawn from the [on exchange unit, 19, via line 21, and is desirably recycled to the process together with make-up brine as required to satisfy the concentration and volume conditions described above for the process. The molybdenum values may be recovered via line 16.

The preparation of the slurry is by ordinary means, including the grinding of the ore or feed material, and usually is carried out in the presence of the brine carrier liquid. The solid-liquid content of the slurry is adjusted as desired, and the'slurry is passed to the process as described above.

VARIABLE Depending upon the particular molybdenum sulfidetype feed source, the operational requirements for a satisfactory electro-oxidation process may vary somewhat. In general, however, the process parameters are as follows:

A Brine (electrolyte), Concentration and Kind The concentration of the electrolyte (salt) may vary from a minor amount, for example 0.1 weight percent up to the saturation value. Best results are, in general, experienced when the concentration is in about the 7 to 20, preferably 9 to weight percent range. The use of brine concentrations above about 15 weight percent and below about 7 percent is relatively inefficient.

Alkali metal, ammonium and alkaline earth metal salts, especially the chlorides (water soluble substantially ionized salts), and mixtures of these salts are satisfactory electrolytes for use in the process. Sodium chloride is preferred for a number of reasons including low cost.

B The Slurry The particle sizing and solids content of the slurry may vary over a substantial range. In general a useful dissolution of molybdenum sulfide values in a pulverized solid feed is experienced when the particles are sized to pass through a 35 mesh screen. The comparative examples 1 4 in Table 1 following, demonstrate, however, that better results are to be expected when at least about percent of the solid particles passes 45 Conditions:

Temp. "C 30 Current Density, 0.5 Amperes per. sq. inch Treatment 4 Amperes 8 Time, hours TABLE 1 Ex no Particle Size Molybdenum 200 mesh 7! dissolved B. (forward) The solid content of the slurry may vary over a wide range. The slurry must be pumpable. For practical purposes at least about 1 part of solid per 100 parts of slurry should be present. In general, good results are obtained when the solid content of the slurry is in the range 1 to parts per 100 parts (weight). A solid content of l to 15 parts to 100 parts solution is preferred when treating higher grade ores or concentrates, whereas a solid content of 30 to 40 parts to 100 parts solution is preferred when treating low grade ores.

C. Slurry pH Molybdenum pH, i.e., values can be electro-oxidized over a large range of pI-I,i.e., from about 1 to l 1.5. Excellent results are in general experienced when the slurry pH is maintained in the range 5 to 9, preferably 5.5. to 6.5. Sulfuric acid is a by-product of the oxidation; therefore in order to maintain the pH, a suitable inorganic base must be added during the course of the oxidative extraction of the molybdenum. Alkali metal and ammonium carbonates and hydroxide and the like are useful for this purpose. A solid such as Na CO I-I O is especially desirable since the addition in the solid form results in no appreciable dilution of the slurry. The contrary is the case where the addition is by the use of an aqueous solution of a suitable base.

The effect of the amount of the base added and the resulting pH is illustrated in examples 5 8 below which were carried out as in example 1 except that the amount of base added was varied as noted in Table 2 with the results as follows:

TABLE 2 Ex. Na cO H o Tails Mo ExtractpH Base Consumption No. grams %Mo ed, lb Na CO /lb Mo cxtd Charge EXAMPLE 9 60 Sohd Feed Pu l g Ore or concentrate Example 7 was repeated except that the slurry was 0 2 Sizing Below 35 Mesh sampled durmg the course of the electro ox1dat1on Electrolyte Aqueous sodium chloride after 2, 3, 3.5 and 4 hours of extract1on t11ne had elapsed and the samples were analyzed with the followtratlon, wt 7o 10 It Slurry, grams mg resu Salt solution, wt.% 90 T. I Sol Feedlwt'qfl 10 me Mo Extracted Base Na CO 2 58 Amount, gr I 3 Time Mo Extracted These data demonstrate that the slurry temperature may vary over a range, i.e, from above the freezing point and below the boiling point of the aqueous brine. Preferably the slurry temperature should be in the range below about 55C and above about C. In the processing of a low-grade ore, temperature control may be effected easily by one or more ordinary electrolysis parameters, including variations in salt concentration, pulp density, current density, size and shape of the cell and the surge tank, and electrode spacing. However, when a molybdenum sulfide concentrate is employed, conventional means such as indirect heat exchangers, cooling towers and the like are desirably used to maintain the slurry temperature below about 55C. E Treatment Rate, Ampere-hours The treatment rate desirably used, varies depending upon the characteristics of the particular ore and slurry being employed. The effect of the rate in the case of the representative low-grade ore described above is demonstrated in examples 14 16 of Table 4 which were carried out as in Example 1 except at different rates as indicated. 1

(1) Current density 0.5 amperes/inch.

Examples 14 16 show that for a given slurry there is an optimum treatment rate which when exceeded results in a less efficient utilization of power. However, a wide range of treatment rates can be employed and yet result in a satisfactory molybdenum dissolution and recovery. The rate desirably used for a particular slurry is readily determinable by routine tests, for example as illustrated in examples 9 11.

F. Current Density The current density, amperes per square inch of electrode, may vary over a range. The use of a current density in the range 0.1 to about 2 amperes per square inch, in general, effects a useful dissolution. However, as illustrated in the examples l7 19 of Table 5 (carried out as Example 1 except with the current density as noted), for a given slurry, electrode spacing and the like, there is an optimium current density (as related to power utilization, cell sizing and capital costs).

TABLE 5 Ex. Current Density Molybdenum No. Amps/inch extracted, "/r

In general, the employment of a current density in the range 0.2 to 1.0 amperes per square inch is most effective and of this range, the use of about 0.5 ampere per square inch is preferred.

G. The Cell The electrolysis unit requirements of the method of the invention may be satisfied by use of a standard cell arrangement and should include sufficient agitation to prevent settling of the particulate solid component of the slurry. The bipolar flow through the type cell as illustrated in the FIGURE is preferred. However, an ordinary plate cell is often advantageously employed, especially for the electro-oxidation of a low grade ore.

Graphite electrodes are in general most satisfactory for use in the method. Other materials of .construction such as copper, iron and the like are also suitable for use in fabricating the cathode. Anodes constructed of PbO or Ru0 coated materials and the like are also suitable.

The spacing between the electrodes may vary somewhat depending upon the particle sizing of the solid, the concentration of the electrolyte and the like. In general a spacing of about one-half inch is satisfactory. H; Time The time required to achieve a satisfactory recovery of the molybdenum and rhenium values in a solid feed varies depending upon the degree of recovery desired,

the brine concentration, the current density used and the like variables. In general a useful recovery can be effected in a process in which the average residence time of the slurry in the cell (electrode portion) is in the range 1 to 20 hours. In general, best results, in terms of economic factors, obtain from the use of average residence times in the range 2.5 to 5 hours.

The foregoing examples were carried out using molybdenum sulfide-type feeds. Essentially the same results are experienced when the feed contains a rhenium sulfide-type component or a mixture or molybdenum and rhenium sulfide materials. Like molybdenum, the rhenium values are conveniently recovered by the use of known ion exchange extraction beds (resins) and techniques (see above listed references). In the case of rhenium, the oxidized form is the sodium (or ammonium, etc.) perrhenate. These examples and the disclosure demonstrate that the method of the invention is a useful effective means for the dissolution of molybdenum and rhenium from sulfide-type solids, ores, tailings or the like, rendering them to a form (i.e., as solutes) from which a facile recovery by ordinary means can be made.

Those of skill in the art in view of the examples and disclosure herein will appreciate that numerous variations in the conditions and feeds and combinations thereof may be made and yet these variations remain within the scope of the claimed invention.

We claim: 1. The method for the dissolution of molybdenum and rhenium, which comprises:

forming a pumpable slurry, said slurry being a mixture of a pulverized solid and a carrier liquid, said solid being a sulfide-type source of molybdenum, or rhenium or of molybdenum and rhenium; and said carrier liquid being an aqueous salt solution; contacting said slurry with an anode and cathode; providing current through said anode and cathode, while maintaining the slurry at a pH of to 9 and temperature of to 55C, and thereby electrolyzing said slurry to electro-oxidize said molybdenum and rhenium; and

8; separating the resulting slurry into two fractions the first of which is an aqueous solution containing dissolved molybdenum, rhenium or a mixture of dissolved molybdenum and rhenium, and the second of which is the depleted electrolyzed solid.

2. The method as in claim 1 where said electrolysis is carried out in a bipolar flow-through cell containing graphite electrodes or in a stirred plate cell.

3. The method as in claim 1 wherein said dissolved molybdenum is removed by an extraction method and the resulting aqueous salt solution is recycled for use in forming a subsequent slurry.

4. The method of claim 1 in which the temperature of the slurry is maintained at about 30 to 50C.

5. The method of claim 1 in which the pH of the slurry is maintained at about 5.5 to 6.5. 

1. THE METHOD FOR THE DISSOLUTION OF MOLYBDENUM AND RHENIUM, WHICH COMPRISES: FORMING A PUMPABLE SLURRY, SAID SLURRY BEING A MIXTURE OF A PULVERIZED SOLID AND A CARRIER LIQUID, SAID SOLID BEING A SULFIDE-TYPE SOURCE OF MOLYBDENUM, OR RHENIUM OR OF MOLYBDENUM AND RHENIUM; AND SAID CARRIER LIQUID BEING AN AQUEOUS SALT SOLUTION; CONTACTING SAID SLURRY WITH AN ANODE AND CATHODE; PROVIDING CURRENT THROUGH SAID ANODE AND CATHODE, WHILE MAINTAINING THE SLURRY AT A PH OF 5 TO 9 AND TEMPERATURE OF 15* TO 55*C, AND THEREBY ELECTROLYZING SAID SLURRY TO ELECTRO-OXIDIZE SAID MOLYBDENUM AND RHENIUM; AND SEPARATING THE RESULTING SLURRY INTO TWO FRACTION THE FIRST OF WHICH IS AN AQUEOUS SOLUTION CONTAINING DISSOLVED MOLYDDENUM, RHENIUM OR A MIXTURE OF DISSOLVED MOLYBDENUM AND RHENIUM, AND THE SECOND OF WHICH IS THE DEPLETED ELECTROLYZED SOLID.
 2. The method as in claim 1 where said electrolysis is carried out in a bipolar flow-through cell containing graphite electrodes or in a stirred plate cell.
 3. The method as in claim 1 wherein said dissolved molybdenum is removed by an extraction method and the resulting aqueous salt solution is recycled for use in forming a subsequent slurry.
 4. The method of claim 1 in which the temperature of the slurry is maintained at about 30* to 50*C.
 5. The method of claim 1 in which the pH of the slurry is maintained at about 5.5 to 6.5. 